1. Field of the Invention
The present invention relates to a track format and record carrier system for use in transferring information to or from a first field on the track that is split by a second field where it is necessary to distinguish the first field from the second field or the information in the first field from the information in the second field.
2. Description of the Related Art
With reference to FIGS. 1A and 1B, a disk record carrier 10 includes a plurality of concentric tracks 12 that are located on one or both sides of the disk record carrier 10. Alternatively, a spiral track can be employed on one or both sides of the disk record carrier 10. Information, in the form of bits 14, are generally established on the tracks in one of two ways. In the first way, bits 14 are established on the tracks 12, as shown in FIG. 1A, at a density per unit length of track that decreases with increasing track radius. Generally, the density varies such that each track 12 has a substantially equal number of bits 14. In the second way, bits 14 are established on the tracks 12 at a density that remains substantially constant with increasing track radius as shown in FIG. 1B. This results in an increasing number of bits 14 per unit length of track as the track radius increases.
With reference to FIGS. 2A and 2B, the bits 14 of information established on the tracks 12 are typically grouped into eight bit units known as bytes 16. A defined number of bytes 16, typically a number that is a power of two, are grouped into a data field 18. In the case where the bits 14 are established on the tracks 12 at a density that decreases with increasing track radius, each track 12 also has an equal number of data fields 18, as shown in FIG. 2A. On the other hand, where the bits 14 are established on the tracks 12 at a density the remains substantially constant from track to track, as shown in FIG. 2B, the number of data fields 18 per track 12 increases with increasing track radius. Associated with each data field 18 is a header 20 that contains information that uniquely identifies the data field 18 and the header 20, the combination of which is hereinafter referred to as a sector 22, with respect to every other sector 22 on the disk record carrier 10. Typically, the information used to identify a particularly sector 22 is the location of the sector 22 on the disk record carrier 10, i.e., the track 12 on which the sector 22 is located and the number of the sector 22 on the track 12. Sectors are typically separated from one another by gaps 23 that insure equal spacing between sectors 22 on a particular track by providing space that can be used to accommodate any overflow in the nominal length of the sector 22 due to deviations in byte length and the like.
Presently, the rotation of disk record carriers is controlled such that a defined point on a track moves at a constant linear velocity (CLV) relative to a read/write (R/W) head or at a constant angular velocity (CAV) where a defined point on a track moves at an increasing linear velocity relative to the R/W head as the radius of the track increases. To transfer information between the disk record carrier and the R/W head at a constant frequency, CLV disk systems establish bits of information on the tracks at a density that remains substantially constant as the track radius increases, as shown in FIG. 1B. In contrast, CAV disk systems establish bits of information on the tracks at a density that decreases as the track radius increases to achieve a constant frequency of information transfer to or from the disk record carrier. Since the bits of information are transferred to or from the disk recording media at a substantially constant frequency in both CLV and CAV disk systems, bytes, data fields, headers, and sectors of information are also transferred between the disk record carrier and the R/W head at a substantially constant frequency.
Recently, disk record carrier systems have been developed where the disk recording media is rotated at a constant angular velocity and the bits of information are established on the tracks at a density that remains substantially constant as the track radius increases. In this type of system, known as a modified constant angular velocity (MCAV) system, information is transferred between the disk recording media and the R/W head at a frequency that increases as the track radius increases. Since bits of information are transferred to or from the disk recording media at a frequency that increases with increasing track radius, bytes, data fields, headers, and sectors of information are also transferred between the disk record carrier and the R/W head at a frequency that increases with increasing track radius.
In addition to including areas for recording user data and identifying the location of a sector, disk record carriers also include servo fields that provide information to one or more servo loops, which typically use the information to control the positioning of the R/W head with respect to the disk record carrier. In large disk systems that include a plurality of disks journaled to a common spindle, one side of one of the disks is typically dedicated to providing the servo information that is used to control the position of the R/W heads associated with the recording surfaces of the other disks. A drawback associated with using an entire surface of a disk to provide servo information is that as the number of the disk recording media on the spindle decreases an increasing portion of the available recording surface becomes dedicated to providing servo information and a decreasing portion is available to store user data. Consequently, in disk systems that have a relatively small number of disk record carriers on a spindle, discrete servo fields have been located on the same recording surface as the data fields. To facilitate the design of the servo loops, among other things, the servo fields are typically established at locations on the tracks such that the servo fields are encountered at a substantially constant frequency. For example, in the case of a CAV disk system, the servo fields are located on each track at an angular interval that remains substantially constant from track to track.
With reference to FIG. 3, a MCAV disk system has been proposed that will utilize a constant frequency servo field 24. The use of a constant frequency servo field 24 with the data fields 18 and/or sectors 22 that are detected by the R/W head at a frequency that increases with increasing track radius results in most, if not all, of the data fields 18 being split by a servo field 24, i.e., a servo field 24 becomes part of the sector 22. Moreover, the location of the servo fields 24 with respect to the beginning or end of the data fields 18 varies in a substantially random fashion from sector to sector. To avoid reading servo data as user data or user data as servo data, the information in the data fields 18 and must be distinguished from the information in the servo fields 24. Similarly, in the case of write operations, the data fields 18 must be distinguished from the servo fields 24 to avoid writing user data in the servo fields 24 or servo data in the data fields 18. One way to discriminate between a data field 18 and a servo field 24 is to provide information on the location of the servo field 24 with respect to a known point in the data field 18. One way to accomplish this is to use a processor that calculates or looks-up in a memory device the number of bytes in the data field 18 that precede or follow the servo field 24, hereinafter referred to as the split count, and provide the split count to a disk controller, which controls the transfer of information to or from the disk record carrier. A major drawback associated with using a processor to determine the split count is that the disk controller must request the split count for each sector to or from which information is to be transferred. Unfortunately, as the frequency at which information is transferred to or from the sectors increases with increasing track radius in the MCAV disk system, the ability of the processor to provide the disk controller with the split count decreases and eventually reaches a point where the processor cannot provide the disk controller with the split count in time for the disk controller to properly transfer the data to or from the disk. Since one of the advantages of using a MCAV disk system is that information can be transferred to or from the disk recording media with increasing frequency as the radius of the tracks increases, the use of a processor to supply the split count adversely affects this advantage.
Based on the foregoing, there is a need for a track format and record carrier system that supports a track format where one field is split by another field and it is necessary to distinguish the first field from the second field or the information in the first field from the information in the second field. Moreover, there is a need for such a track format and record carrier system where the drawbacks associated with using a processor or other device to determine the split count and provide the split count to a disk controller are reduced or substantially eliminated. More specifically, there is a need for a track format and record carrier system for use in distinguishing servo fields from data fields in MCAV disk systems that employs a constant frequency servo field.